102 DWIGHT 



that only by a radical rearrangement and delimitation of the terms 

 used may further confusion be avoided. The chief thing to bear 

 in mind is that every species passes through a definite series of 

 plumages and a definite series of moults, each plumage being 

 succeeded either by a moult or the place of the moult may be 

 taken by wear alone. There is no theory about this cardinal 

 principle and there are ample facts to support it. Of many spe- 

 cies, I have examined specimens taken every month in the year 

 showing not only the sequence of plumages and moults but all 

 of the intermediate steps by which the plumage has been ac- 

 quired or modified. With an abundance of material there is 

 not the slightest difficulty in explaining plumages, but in many 

 species there are gaps which careful study of the feathers and 

 the application of fundamental principles must be trusted to 

 fill. For instance, when the Scarlet Tanagers (Piranga erytliro- 

 melas) leave the vicinity of New York towards the end of Sep- 

 tember, all of them are in the olive green body plumage of the 

 female, the young males with similarly colored wings and tails, 

 the adults with black wings and tails. When the males return 

 in May all are in bright scarlet dress with black tails, but a 

 certain number of them have worn brown wing quills. The 

 red feathers examined under a glass are quite as fresh as the 

 green ones seen in September. If the wings are examined, 

 both the brown and the black quills will show wear, the black 

 least as might be expected from their color. If the tails are 

 examined those of the black-winged birds are slightly worn, 

 those of the brown-winged fresh and new. It is a perfectly 

 natural inference that the brown-winged birds are young males 

 and that they have acquired the red body plumage and the 

 black tail by a recent moult while the adults have not moulted 

 the wings and tail, but merely assumed the red body plumage. 

 Further evidence in support of this conclusion is afforded by 

 patches of worn green feathers left over among the red, such 

 feathers occurring most frequently in the brown-winged young 

 birds and finally we sometimes find red feathers still invested 

 with their scaly sheaths. The only gap left is a Tanager show- 

 ing extensive moult, and it is safe to predict that such a speci- 



